In motor vehicle engineering, “brake-by-wire” brake systems are becoming ever more widespread. Such brake systems often comprise not only a master brake cylinder which can be actuated by the vehicle driver but also an electrically controllable pressure supply device by means of which the wheel brakes or the master brake cylinder is actuated in the “brake-by-wire” operating mode. In order to give the vehicle driver a pleasant pedal sensation in the “brake-by-wire” operating mode, the brake systems usually comprise a brake pedal sensation simulation device. In these brake systems, the wheel brake can also be actuated on the basis of electronic signals, without active involvement of the vehicle driver. These electronic signals can, for example, be output by an electronic stability program or a distance control system.
International patent application WO 2011/029812 A1, which is incorporated herein by reference, discloses a “brake-by-wire” brake system with a master brake cylinder which can be actuated by a brake pedal, a travel simulator and a pressure supply device. In a “brake-by-wire” operating mode pressure is applied to the wheel brakes by the pressure supply device. In a fallback operating mode, pressure is applied to the wheel brakes by means of the master brake cylinder which can be actuated by the brake pedal. In the application, no further details are given as to whether and, if appropriate, how a changeover can be carried out from the fallback operating mode into the “brake-by-wire” operating mode.